In the related art, wind turbine generators that generate electricity by utilizing wind force, which is natural energy, are known. A wind turbine generator of this type is provided with a rotor head, which is provided on a nacelle mounted on a tower and has wind-turbine rotor blade attached thereto, a main shaft connected to this rotor head so as to rotate together therewith, a speed-increasing gearbox connected to the main shaft that rotates in response to wind force received by the wind-turbine rotor blade, and a generator driven by a shaft output of the speed-increasing gearbox. In a wind turbine generator having such a configuration, the rotor head, which is equipped with the wind-turbine rotor blade that convert wind force into torque, and the main shaft rotate so as to generate a shaft output, and the shaft output is increased in rotation speed via the speed-increasing gearbox connected to the main shaft and is transmitted to the generator. Therefore, the shaft output obtained by converting wind force into torque acts as a driving source for the generator, whereby electricity can be generated by utilizing the wind force as power for the generator.
Normally, in the wind turbine generator of the related art described above, a drive train equipped with the speed-increasing gearbox and the generator is disposed inside the nacelle. For this reason, a frame such as a nacelle bedplate that supports the drive train has a relatively heavy structure for ensuring, for example, an installation space for the drive train. In the case of a single-bearing structure, it is difficult to support the rotor head during replacement of the speed-increasing gearbox since it also serves as a support structure for the rotor head.
There is also a structure in which the generator is disposed between a rotor and the nacelle, the generator in this case is non-replaceable.
For the purpose of reducing the size and weight of the nacelle, there has been proposed a configuration in which the drive train extending from the main shaft to the generator via the speed-increasing gearbox is installed inside the rotor head (for example, see Patent Document 1).